George, what compression ratio are you running and what fuel flow ?
I find with the more combustion pressure you run the more ign you need.
If you are running 13 to 1 compression, and under 2 gpm fuel flow you may not need a mag.
As far as the weight of an on-board battery to power your dist ign, you could go with lighter battery, I sell a 12 volt, 550 amp battery that weights under 5 lbs. And MSD said a 7al only needs a 12-15 amp battery, which I can get that weighs 1 lb.
I'm sure Spud can fill-in some details, on mag vs dist ign systems.
Jon, Hayden Wheels, 800-624-3803